Ethene/norbornene copolymerization by [Me2Si(3-tertBuCp)(NtertBu)]TiCl2/MAO-catalyst

Ethene/norbornene copolymerization by the catalyst system [Me₂Si(3-^tertBuCp)(N^tertBu)]TiCl₂/MAO was investigated in detail at 30 °C, 60 °C, and 90 °C. A mass flow controller was used in this work to obtain kinetic data and investigate temperature's effects on activity, norbornene incorporation, copolymerization parameter, microstructure, glass transition temperature, and molar masses were described. High copolymerization valuesr _ξ and high alternation are determined. The number of isotactic alternating sequences is much higher than that of the syndiotactic alternating sequences.     

Application of digital image correlation to full-field measurement of shrinkage strain of dental composites

Objectives: Polymerization shrinkage of dental composites remains a major concern in restorative dentistry because it can lead to micro-cracking of the tooth and debonding at the tooth-restoration interface. The aim of this study was to measure the full-field polymerization shrinkage of dental composites using the optical digital image correlation (DIC) method and to evaluate how the measurement is influenced by the factors in experiment setup and image analysis. Methods: Four commercial dental composites, Premise Dentine, Z100, Z250 and Tetric EvoCeram, were tested. Composite was first placed into a slot mould to form a bar specimen with rectangular-section of 4 mm mm, followed by the surface painting to create irregular speckles. Curing was then applied at one end of the specimen while the other part were covered against curing light for simulating the clinical curing condition of composite in dental cavity. The painted surface was recorded by a charge-coupled device (CCD) camera before and after curing. Subsequently, the volumetric shrinkage of the specimen was calculated with specialist DIC software based on image cross correlation. In addition, a few factors that may influence the measuring accuracy, including the subset window size, speckle size, illumination light and specimen length, were also evaluated. Results: The volumetric shrinkage of the specimen generally decreases with increasing distance from the irradiated surface with a conspicuous exception being the composite Premise Dentine as its maximum shrinkage occurred at a subsurface distance of about 1 mm instead of the irradiated surface. Z100 had the greatest maximum shrinkage strain, followed by Z250, Tetric EvoCeram and then Premise Dentine. Larger subset window size made the shrinkage strain contour smoother. But the cost was that some details in the heterogeneity of the material were lost. Very small subset window size resulted in a lot of noise in the data, making it difficult to discern the general pattern in the strain distribution. Speckle size did not seem to have obvious effect on the volumetric shrinkage strain along specimen length; however, larger speckles resulted in higher level of noise or heterogeneity in the shrinkage distribution. Compared with bright illumination, dimmer lighting produced larger standard deviations in the measured shrinkage, indicating a higher level of noise. The longer the specimen, the greater was the rate of reduction with distance from the irradiated surface, especially for the longitudinal strain. Significance: The image correlation method is capable of producing full-field polymerization shrinkage of dental composites. The accuracy of the measurements relies on selection of optimal parameters in experimental setup and DIC analysis.     

乳化液泵的研究现状与发展

乳化液泵是流体传动领域的重要研究方向,符合节能、环保、可持续发展的要求,具有很广泛的应用前景。该文阐述了乳化液泵的发展历史,并介绍了国内外的研究进展,以及乳化液泵在国民经济中各个领域中的应用。     

Gel time of calcium acrylate grouting material

INTRODUCTION One of the main advantages of chemical groutsis easy control of gel time (Mollamahmutoglu andLittlejohn, 1996; ?nupárek and Soucek, 2000).Calcium acrylate is a chemical grout usually used ingeotechnical engineering (Zelanko and Karfakis,1997), and is a water-soluble monomer that po-lymerizes in an aqueous solution. The rate of po-lymerization is controlled by the concentration ofcatalyst and activator. The polymerization of cal-cium acrylate is free radical chain pol…     

新型金属切削液的研制

根据金属切削液的基本理论和发展趋势,针对金属切削乳化油存在的不足,提出了采用20#机械油作基础油、采用精脂酸和松香与混合碱(NaOH和KOH按1∶1质量比形成的混合物)反应后形成的混合皂作乳化剂、采用低分子醇(如乙醇)作乳化稳定剂、加入复合型的防锈剂和极压剂来生产新型金属切削液方案,通过单因素实验方法和正交实验方法对乳化剂、防锈剂、稳定剂和极压剂进行了比选,确定出了适宜的乳化剂、防锈剂、稳定剂和极压剂及其用量．     

乳状液膜法处理苯胺废水的实验室研究

研究了苯胺水溶液的乳化液膜处理过程,对溶剂和表面活性剂的选择及用量、膜增强剂用量、搅拌速度、乳水比(Rew)、油内比(Roi)、外相pH值及处理时间的影响进行一系列的研究.结果表明,在适宜的操作条件下,当水中苯胺浓度为510.8 mg/L时,经过一级液膜处理,水中苯胺的含量可降到1.405 mg/L,苯胺去除率可达99%以上,达到国家二级排放标准.     

Gel time of calcium acrylate grouting material

Calcium acrylate is a polymerized grout, and can polymerize in an aqueous solution. The polymerizationreaction utilizes ammonium persulfate as a catalyst and sodium thiosulfate as the activator. Based on the theory of reactionkinetics, this study on the relation between gel time and concentration of activator and catalyst showed that gel time ofcalcium acrylate is inversely proportional to activator and catalyst concentration. A formula of gel time is proposed, and anexample is provided to verify the proposed formula.     

Ethene/norbornene copolymerization by [Me2Si(3-tertBuCp)(NtertBu)]TiCl2/MAO-catalyst

Ethene/norbornene copolymerization by the catalyst system [Me2Si(3-tertBuCp)(NtertBu)]TiCl2/MAO was investigated in detail at 30℃, 60℃, and 90℃. A mass flow controller was used in this work to obtain kinetic data and investigate temperature's effects on activity, norbornene incorporation, copolymerization parameter, microstructure, glass transition temperature, and molar masses were described. High copolymerization values rE and high alternation are determined. The number of isotactic alternating sequences is much higher than that of the syndiotactic alternating sequences.     

经纱浆料聚合物的分子设计考虑

本文就纤维材料、浆料工艺特性、环境因素、竞聚率及聚合工艺等方面对聚合物经纱浆料的分子设计作了较为详尽的分析,提出了经纱浆料聚合物分子设计的一些依据。     

Cossee单金属定向聚合催化机理

本文详细阐述了Cossee单金属定向聚合催化机理,包括催化活性中心结构、链增长机理、分子轨道理论处理和主要的实验证据等,供教学参考.